SAN YSIDRO  A group of about 100 people trying to illegally cross the border Sunday near the San Ysidro port of entry threw rocks and bottles at U.S. Border Patrol agents, who responded by using pepper spray and other means to force the crowd back into Mexico, federal officials said.

The incident has raised concerns among advocates on both sides of the immigration debate, as well as Border Patrol representatives.

Immigrant-rights groups in San Diego said they didn’t know beforehand about the plan to rush the border, and they worry that desperation is driving homeless deportees to make a bold bid to rejoin their families in the United States.

Border-security groups see this situation as evidence that the border remains unsecured, something they said should be fixed before Congress considers proposals to grant legal status to unauthorized immigrants.

And Border Patrol representatives worry that Sunday’s confrontation could be a political protest, which they said agents want to avoid — especially when it involves the potential for loss of life.

The incident occurred about a quarter-mile west of the San Ysidro border crossing in the Tijuana River channel. No one was seriously injured, no shots were fired and no arrests were made, said Mary Beth Caston, a Border Patrol spokeswoman.

The group first approached a lone agent stationed about 1/8 of a mile north of the border. They ignored his commands to stop, so he fired pepper balls to try to stop them and protect himself, Caston said.

As the crowd kept advancing and throwing rocks and bottles, she said, more agents came to the scene and used other “intermediate use-of-force devices” to push back the group. The agents also contacted Mexican law enforcement.

Tijuana’s top police officer, Public Safety Secretary J. Alberto Capella, said “There is no information that we can provide.” He referred questions to the U.S. Border Patrol.

The spokesman for Tijuana police, Rafael Morales, said the agency’s officers did not intervene and had no knowledge of the incident.

Caston said several agents were struck in the arms and legs with rocks, and that one agent was hit in the head with a filled water bottle.

“While attacks on Border Patrol agents are not uncommon, the agents showed great restraint when faced with the dangers of this unusually large group, and fortunately no one was serious injured,” said Paul Beeson, San Diego sector chief for the Border Patrol.

The agency did not specify the time of Sunday’s incident.

This type of rush on the border has not been seen since the late 1980s and early ’90s, when groups of border-crossers would run into the U.S. while agents tried to apprehend as many people as possible. The practice mostly disappeared after Operation Gatekeeper began in 1994 and brought with it tall fences, walls and more agents.

“If it was a protest, it was a really stupid way to go about it because there were individuals who started throwing rocks and other projectiles,” said Shawn Moran, vice president of the National Border Patrol Council. “It’s not the right venue; agents do not enact legislation, don’t write laws or write polices. If protesters want to address Congress and try to change laws, so be it.”